The invention relates to missiles generally, and more particularly, to a polarized semi-active laser last pulse logic missile seeker.
Conventional semi-active laser last pulse logic (SALLPL) missile seekers, staring imaging infrared (I2R) focal plane arrays, and their use together to detect and track missile targets, are known in the art. For example, U.S. Pat. No. 6,111,241 ('241 patent), issued to English et al., sets forth and describes combining semi-active laser last pulse logic signal processing using a single PIN photodiode with a staring imaging infrared focal plane array to effectuate a more accurate and direct impact of a Hellfire missile on a laser-illuminated target.
A weakness in the system described in the '241 patent is that the temporal and spatial laser returns (e.g. laser energy reflected, or scattered, from the laser-illuminated target) are often difficult to distinguish from background and/or jamming radiation, commonly called “clutter”, existing at or near the target location. Clutter interferes with the temporal and spatial laser returns and renders target acquisition and tracking difficult. However incorporating polarization as described and claimed herein will enhance the target discrimination capability of conventional SALLPL seekers.
As described in U.S. Pat. No. 6,310,345 ('345 patent) issued to Pittman et al., infrared polarimetry is a technique for acquiring and processing emissive and scattered radiation in the infrared bands. A relatively new and slowly maturing technology, infrared polarimetry is limited by polarization aberrations, scattering and birefringence effects introduced by extant instrumentation.
As described in the '345 patent, infrared polarimetry can be used to enhance the discrimination of targets from clutter, but use has been limited to conventional forward looking infrared (FLIR) camera systems, such as those produced by FLIR Systems of Boston, Mass. These conventional systems detect and convert infrared energy (heat) into an electronic signal, which is then processed to produce a thermal image which can be displayed on a video monitor.
Because conventional FLIR camera systems differ significantly from semi-active laser last pulse missile seekers in components, operation and application, it is desirable to adapt and apply infrared polarimetry technology to a SALLPL missile seeker, which utilizes a staring imaging infrared focal plane array, in a manner that enhances the SALLPL missile seeker's ability to acquire and track laser-illuminated targets and distinguish such targets from clutter.